Moparts

Ideal AFR at wot?

Posted By: Dart 340

Ideal AFR at wot? - 06/17/09 09:40 PM

Can someone give me an idea of what the ideal
AFR would be under wot? I am running around
11-12 and think that is about perfect but not
sure if it's still a little rich. I have my
idle circuit at 14.5 and cruising at 55 mph
also at 14.5

Thanks.
Posted By: Anonymous

Re: Ideal AFR at wot? - 06/17/09 10:32 PM

The ideal A/F ratio is the one that makes the most power, either on the dyno, or at the drag strip (MPH)...........It can be anywhere from 10.9 to 1 to somewhere in the mid 13's.........and it all boils down to fuel fall out.......How good the fuel distribution of the intake is and how fast the air speed is through the port........

What's your motor build up??? What heads?
Posted By: Dartman75

Re: Ideal AFR at wot? - 06/18/09 12:15 AM

Since I can change the AFR of my motor on a whim quite easily, I have played a lot with my motor. My motor definitiely starts to choke on more than about 12, and by 10 ti's flat falling on it's face. 13.5 is ideal I thinkhigh twelves to about 13.8.

Other factors play into things that will make it challenge to get WOT perfect across all the RPM ranges. For anythign other than WOT 13.5 to 16 isvery runnable for crusing and very light throttle. I run as lean as 17-18 for long highway stints at cruise, but that's how I get 18MPH from a ~600 horsie motor.

Greg
Posted By: Anonymous

Re: Ideal AFR at wot? - 06/18/09 02:33 AM

Quote:

.........but that's how I get 18MPH from a ~600 horsie motor.

Greg



Sorry to hijack......but is that from the small block in your sig pic? If so, have you raced it? If so, what MPH has it run?
Posted By: Dart 340

Re: Ideal AFR at wot? - 06/18/09 02:33 AM

Quote:

The ideal A/F ratio is the one that makes the most power, either on the dyno, or at the drag strip (MPH)...........It can be anywhere from 10.9 to 1 to somewhere in the mid 13's.........and it all boils down to fuel fall out.......How good the fuel distribution of the intake is and how fast the air speed is through the port........

What's your motor build up??? What heads?



I have a 340 punched .060 over, cylinder pressure
is 190 psi cranking, running stock heads, eddy
air gap rpm manifold, and eddy performer rpm cam.
Carb is a street avenger 670. Running a pertronix
ignition but thinking about a msd box.

The car feels light under wot at 13.5-14 but was
thinking it might make more power set richer.
It does feel more labored running down at 10.5 or
so.
Posted By: Anonymous

Re: Ideal AFR at wot? - 06/18/09 02:36 AM

Off the top of my head, I'd guess the A/F for max power would need to be in the low to high 12 range.........maybe low 13's........but I'd stay a little on the rich side on a pump gas, street car........
Posted By: Barnstorm

Re: Ideal AFR at wot? - 06/18/09 02:46 AM

My dyno sheets say 820hp @7200..700tq@5200 AF 12.98....500 wedge.

Attached picture 5299766-mopar_resize.jpg
Posted By: Aspen7695

Re: Ideal AFR at wot? - 06/18/09 03:00 AM

The 360 in my Duster runs best between 12.7 and 13. It slows down as soon as it gets to 12.5 or lower,especially when the humidity gets above 20%.

Raul
Posted By: Dart 340

Re: Ideal AFR at wot? - 06/18/09 03:05 AM

Thanks guys, all good information.

I am having trouble wrapping my head around why my
carb runs perfect 14.5 at 2500 rpms at 5 mph but
at 3200 rpm at 702 mph it is running at 12.5
Since I am not loading the motor, should I not still
be on the primaries only? and the powervalve should
not be open either correct?
Posted By: SCATPK

Re: Ideal AFR at wot? - 06/18/09 05:14 AM

I have been told that most motors make the most power somewhere between 12.8 - 13.2 a/f wot.
Posted By: JimG

Re: Ideal AFR at wot? - 06/18/09 11:30 AM

Quote:

Thanks guys, all good information.

I am having trouble wrapping my head around why my
carb runs perfect 14.5 at 2500 rpms at 5 mph but
at 3200 rpm at 702 mph it is running at 12.5
Since I am not loading the motor, should I not still
be on the primaries only? and the powervalve should
not be open either correct?



I assume you mean
14.5 - 2500 RPM - 55 MPH
12.5 - 3200 RPM - 70 MPH

Does it get progressively worse as you speed up even more? Which primary PV are you running, and what is the vacuum at 2500/55 and 3200/70. You can temporarily, as a test, block the PV with a plug and see if the problem persists.

If it's not the PV, and if it gets progressively worse (or doesn't lean out) as speed/RPM increases further, larger Main Air Bleeds may be in order. Be aware that larger MABs might cause it to run pig rich at very light throttle/load. How's the AFR now at 2-5% throttle at light load?

Jim
Posted By: Dart 340

Re: Ideal AFR at wot? - 06/18/09 02:29 PM

Quote:



I assume you mean
14.5 - 2500 RPM - 55 MPH
12.5 - 3200 RPM - 70 MPH

Does it get progressively worse as you speed up even more? Which primary PV are you running, and what is the vacuum at 2500/55 and 3200/70. You can temporarily, as a test, block the PV with a plug and see if the problem persists.

If it's not the PV, and if it gets progressively worse (or doesn't lean out) as speed/RPM increases further, larger Main Air Bleeds may be in order. Be aware that larger MABs might cause it to run pig rich at very light throttle/load. How's the AFR now at 2-5% throttle at light load?

Jim



I will have to check vacuum and get back to you
on that. The primary PV I have is a 5.5 standard
not a high flow valve. I run 11 InHg at idle so
I thought that would be really close to the right
one. I've jetted the carb from the stock 65's to
68's because it was running well into the 16's
at 2500 rpm before and now it's right about 14.5

I will get it out on the highway and see if it
gets richer, but from memory it doesn't cruising
but running wot for extended time get it down into
low 11's. I have 68's in the secondaries but
didn't want to go smaller yet. Initial wot gives
a low 14 for about 2 seconds then she goes to
low 11's. Should I wire shut the secondaries and
see how it goes? was thinking she would run way
lean at higher rpms.
Posted By: JimG

Re: Ideal AFR at wot? - 06/18/09 03:11 PM

Quote:

The primary PV I have is a 5.5 standard
not a high flow valve.



OK, that means it's open at vacuum levels below 5.5 in hg (and is richening the mixture), and closed at vacuum levels above 5.5. This assumes the PV is working properly. Put a vacuum gauge in the car and be sure the vacuum doesn't drop below 5.5 at 3200/70 mph when it goes rich. Not likely, but you need to know.

Quote:

I run 11 InHg at idle so I thought that would be really close to the right
one.



Don't get too hung up on idle vacuum vs. PV rating. You've got a wideband meter - choose the power valve that opens when heavy throttle/heavy load causes the mixture to go lean. You seem to be having the opposire problem, however.

Quote:

I've jetted the carb from the stock 65's to
68's because it was running well into the 16's
at 2500 rpm before and now it's right about 14.5
I will get it out on the highway and see if it
gets richer, but from memory it doesn't cruising
but running wot for extended time get it down into
low 11's. I have 68's in the secondaries but
didn't want to go smaller yet. Initial wot gives
a low 14 for about 2 seconds then she goes to
low 11's.



Forget about the secondaries and WOT AFR for now - save that for last. It's too rich at WOT, and that's good - for now. Rich is safe. If you plan on messing with the primary side, you'll probably make changes that will ultimately upset the WOT readings. Work on getting the primary side right, then when you're sure it's just like you want it, work on the secondary side. To work on the seondary side now is a waste of effort and time.


Quote:

Should I wire shut the secondaries and
see how it goes? was thinking she would run way
lean at higher rpms.



Only if you think they're popping open at 3200 and causing your rich condition. This must be a vacuum secondary carb, right? Does it have screw in air bleeds or pressed in?

If you're in the 14 neighborhood at 2500, you're halfway home!
Posted By: Dartman75

Re: Ideal AFR at wot? - 06/18/09 08:05 PM

Quote:

Quote:

.........but that's how I get 18MPH from a ~600 horsie motor.

Greg



Sorry to hijack......but is that from the small block in your sig pic? If so, have you raced it? If so, what MPH has it run?



It's the updated flavor of the one in my pic. Slightly out of date pic here: http://www.telusplanet.net/public/zbhansen/temp/DartNewMotorInstalled.JPG
It's making 18MPG pure highway leaned right out, city is a whole different ball game mostly due to excessive sitting parked at red lights. The previous build (the one in the current sig pic with the RPM air-gap ran 12.69@109.5MPH at 3600DA, traction limited, and throttle body restricted). I fired my throttle body and traction issues, only to bend a valve resulting in the rebuild for a few extra ponies while I was at it. The sig pic motor was good for about 450 crank, and the new mill I expect around 600 crank. The new updated mill will make it to the track in mid july, once I get on e chassis dyno (July 7th) to make sure the hihger RPM's are tuned correctly before I break something again.

We now return you to your regularily scheduled forum content.

Greg
Posted By: 67HEMI

Re: Ideal AFR at wot? - 06/19/09 12:40 PM

Mine runs the quickest at 12.6 to 12.8.
Posted By: 67HEMI

Re: Ideal AFR at wot? - 06/19/09 12:43 PM

Quote:

The 360 in my Duster runs best between 12.7 and 13. It slows down as soon as it gets to 12.5 or lower,especially when the humidity gets above 20%.

Raul



Above 20%? Man it never gets below 60% here in Mississippi!
Posted By: Dragula

Re: Ideal AFR at wot? - 06/19/09 04:02 PM

I have also found 12.7-12.8 runs best in my stroked hemi at WOT.

I have a 340 I will be switching over to EFI, maybe this year, so I want to get an A/F gauge on it now while its still carbed to see where it likes to be. Still trying to figure out my runs from last week where I thought it was a touch rich at Test & Tune on a mid 60* day and then went racing on Sunday at 85* day, and mph picked up and it spun the slicks out of the hole everytime and yet still went a 1/10th quicker. Its either the 10% ethanol fuel, or it was actually a little lean at Test & Tune. The fuel in the tank tuesday was pretty much left over from the previous year and I am pretty sure contained no ethanol.

Either way, I liked the results at the traps. Now I just need to find a way to get more traction.
© 2024 Moparts Forums